Liquid crystal display device and electronic apparatus

ABSTRACT

A liquid crystal display device according to the present disclosure includes: a liquid crystal unit including a pixel electrode, a counter electrode facing the pixel electrode, and a liquid crystal layer sealed between the pixel electrode and the counter electrode; a first writing circuit configured to write a positive polarity video signal among video signals whose polarity changes periodically; and a second writing circuit configured to write a negative polarity video signal among the video signals whose polarity changes periodically. The liquid crystal unit, the first writing circuit, and the second writing circuit are provided for each pixel. The first writing circuit and the second writing circuit include transistors having conductivity types different from each other.

TECHNICAL FIELD

The present disclosure relates to a liquid crystal display device and anelectronic apparatus.

BACKGROUND ART

As one of liquid crystal display devices, there is a liquid crystaldisplay device in which a video signal is alternately written in twosystems of positive polarity and negative polarity for each pixel, anddisplay driving is performed on the basis of the written video signalsof the two systems. (See, for example, Patent Document 1).

CITATION LIST Patent Document

-   Patent Document 1: Japanese Patent Application Laid-Open No.    2010-231179

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

In the prior art described in Patent Document 1 (Japanese PatentApplication Laid-Open No. 2010-231179), two systems of writing circuitsfor alternately writing a positive polarity video signal and a negativepolarity video signal are configured by transistors of the sameconductivity type, specifically only N-channel MOS transistors. In thiscase, the voltage drop due to a threshold voltage V_(th) of theN-channel MOS transistor has an influence, which leads to lowering of aliquid crystal drive voltage on the negative side.

Therefore, an object of the present disclosure is to provide a liquidcrystal display device capable of preventing a liquid crystal drivevoltage from lowering due to a threshold voltage V_(th) of a transistorthat configures a video signal writing circuit, and an electronicapparatus including the liquid crystal display device.

Solutions to Problems

A liquid crystal display device of the present disclosure for achievingthe object described above includes:

a liquid crystal unit including a pixel electrode, a counter electrodefacing the pixel electrode, and a liquid crystal layer sealed betweenthe pixel electrode and the counter electrode;

a first writing circuit configured to write a positive polarity videosignal among video signals whose polarity changes periodically; and

a second writing circuit configured to write a negative polarity videosignal among the video signals whose polarity changes periodically,

the liquid crystal unit, the first writing circuit, and the secondwriting circuit provided for each pixel, and

the first writing circuit and the second writing circuit includingtransistors having conductivity types different from each other.Furthermore, an electronic apparatus of the present disclosure forachieving the object described above includes the liquid crystal displaydevice having the above configuration.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a system configuration diagram illustrating an example of thesystem configuration of a liquid crystal display device of the presentdisclosure.

FIG. 2 is a circuit diagram illustrating a circuit example of a pixelcircuit according to a reference example.

FIG. 3A is a waveform diagram illustrating voltage waveforms of a videosignal V_(sig) and a common voltage V_(com) during white display, andFIG. 3B is a waveform diagram illustrating voltage waveforms of a videosignal V_(sig) and a common voltage V_(com) during black display, in apixel circuit according to a reference example.

FIG. 4 is a circuit diagram illustrating a circuit example of a pixelcircuit according to Example 1.

FIG. 5A is a waveform diagram illustrating voltage waveforms of a videosignal V_(sig) and a common voltage V_(com) during white display, andFIG. 5B is a waveform diagram illustrating voltage waveforms of a videosignal V_(sig) and a common voltage V_(com) during black display, in apixel circuit according to Example 1.

FIG. 6 is a characteristic diagram illustrating avoltage-reflectance/transmittance characteristic of liquid crystal.

FIG. 7 is a circuit diagram illustrating a circuit example of a pixelcircuit according to Example 2.

FIG. 8 is a circuit diagram illustrating a circuit example of a pixelcircuit according to Example 3.

FIG. 9 is a sectional view illustrating an example of a sectionalstructure of a LCOS device according to Example 4.

FIG. 10 is a schematic configuration diagram illustrating a basicconfiguration of a projection-type display device (projector) accordingto Specific example 1 of an electronic apparatus of the presentdisclosure.

FIG. 11 is an external view illustrating an example of a head mounteddisplay according to Specific example 2 of the electronic apparatus ofthe present disclosure.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a mode for carrying out the technology of the presentdisclosure (hereinafter, referred to as an embodiment) will be describedin detail with reference to the drawings. The technology of the presentdisclosure is not limited to the embodiment, and various numericalvalues, materials, and the like in the embodiment are examples. In thefollowing description, the same elements or elements having the samefunction will be denoted by the same reference signs, and an overlappingdescription will be omitted. Note that the description will be given inthe following order.

1. General description of liquid crystal display device and electronicapparatus of present disclosure

2. Liquid crystal display device to which technology of presentdisclosure is applied

3. Basic configuration of liquid crystal display device

3-1. System configuration

3-1-1. V_(com) inversion driving

3-1-2. Surface collective driving

3-2. Pixel circuit according to reference example

4. Liquid crystal display device according to embodiment

4-1. Example 1 (Example of case where liquid crystal mode is VA mode)

4-2. Example 2 (Example of case where liquid crystal mode is TN mode)

4-3. Example 3 (Modification of Example 1: Example using transfer gate)

4-4. Example 4 (Example of LCOS device)

5. Electronic apparatus of present disclosure

5-1. Specific example 1 (Example of projection-type display device)

5-2. Specific example 2 (Example of head mounted display)

6. Configurations that present disclosure can take

<General Description of Liquid Crystal Display Device and ElectronicApparatus of Present Disclosure>

A liquid crystal display device and an electronic apparatus of thepresent disclosure may have a configuration in which a common voltagewhose polarity is periodically inverted in synchronization with apositive polarity video signal and a negative polarity video signal isbe applied to a counter electrode of a liquid crystal unit in common forall the pixels.

The liquid crystal display device and the electronic apparatus of thepresent disclosure including the preferred configuration as describedabove may have a configuration in which a first writing circuit and asecond writing circuit have storage capacitors that hold a positivepolarity video signal and a negative polarity video signal,respectively. Moreover, the first writing circuit and the second writingcircuit may include first transfer transistors that alternately write apositive polarity video signal and a negative polarity video signal tothe storage capacitors, and second transfer transistors that alternatelyapply held voltages of the storage capacitors to the pixel electrode ofthe liquid crystal unit collectively for all the pixels.

Moreover, the liquid crystal display device and the electronic apparatusof the present disclosure including the preferred configuration asdescribed above may have a configuration in which in a case where aliquid crystal mode is a VA mode, each of the first transfer transistorand the second transfer transistor of the first writing circuit includesan N-channel transistor and each of the first transfer transistor andthe second transfer transistor of the second writing circuit includes aP-channel transistor. Alternatively, a configuration may be adopted inwhich in a case where a liquid crystal mode is a TN mode, each of thefirst transfer transistor and the second transfer transistor of thefirst writing circuit includes a P-channel transistor and each of thefirst transfer transistor and the second transfer transistor of thesecond writing circuit includes an N-channel transistor.

Furthermore, the liquid crystal display device and the electronicapparatus of the present disclosure including the above-describedpreferred configuration may have a configuration in which a thresholdvoltage of the first transfer transistor of each of the first writingcircuit and the second writing circuit is equal to or lower than athreshold voltage of a voltage-reflectance/transmittance characteristicof liquid crystal. Furthermore, the first transfer transistor of each ofthe first writing circuit and the second writing circuit may include atransfer gate in which an N-channel transistor and P-channel typetransistor are connected in parallel.

In addition, the liquid crystal display device and the electronicapparatus of the present disclosure including the above-describedpreferred configuration may have a configuration in which the liquidcrystal unit, the first writing circuit, and the second writing circuitare formed on a semiconductor substrate.

<Liquid Crystal Display Device to which Technology of Present Disclosureis Applied>

First, a liquid crystal display device to which the technology of thepresent disclosure is applied will be described.

The liquid crystal display devices are classified into a transmissivetype, a reflective type, and a semi-transmissive type with respect to adisplay system. In addition, as examples of a material used for a thinfilm transistor (TFT) used for a pixel, silicon, a transparent oxidesemiconductor (TOS), an organic semiconductor, and the like can bementioned.

Furthermore, in a transmissive-type liquid crystal display device,amorphous silicon (noncrystalline semiconductor) or poly-silicon(polycrystalline semiconductor) is often used as a silicon material. Ina reflective-type liquid crystal display device, single crystal siliconis often used. Note that poly-silicon is classified into hightemperature poly-silicon (HTPS) that forms a thin film in ahigh-temperature environment of 1000 degrees Celsius or higher, and lowtemperature poly-silicon (LTPS) that forms a thin film in alow-temperature environment of 600 degrees Celsius or lower.

In a liquid crystal panel, a transparent substrate having alight-transmissive property such as a quartz substrate, a glasssubstrate, or a silicon substrate is used as a substrate on which liquidcrystal is disposed. In general, a glass substrate is used in anamorphous silicon-transmissive type liquid crystal panel or a lowtemperature poly-silicon-transmissive type liquid crystal panel, aquartz substrate is used in a high temperature poly-silicon-transmissivetype liquid crystal panel, and a silicon substrate is used in a singlecrystal silicon-reflective type liquid crystal panel. A device in whichliquid crystal is disposed on a silicon substrate is generally calledliquid crystal on silicon (LCOS).

A liquid crystal mode (liquid crystal molecule arrangement) includes avertical alignment (VA) mode and a twisted nematic (TN) mode. The VAmode is normally black in which transmittance or reflectance isminimized and the screen becomes black when no voltage is applied to theliquid crystal. The TN mode is normally white in which the transmittanceor the reflectance is maximized and the screen becomes white when novoltage is applied to the liquid crystal.

Furthermore, a TFT process includes high temperature poly-silicon, lowtemperature poly-silicon, and amorphous silicon (a-Si). In a liquidcrystal panel for a projection-type display device (projector), the VAmode is often selected as the liquid crystal mode, and high temperaturepoly-silicon (HTPS) is often selected as the TFT process (so-calledHTPS-liquid crystal panel). In small and medium-sized direct-view liquidcrystal panels, the VA mode is often selected as the liquid crystalmode, and low temperature poly-silicon (LTPS) is often selected as theTFT process (so-called LTPS-liquid crystal panel). In large-sizeddirect-view liquid crystal panels, the VA mode is often selected as theliquid crystal mode, and amorphous silicon is often selected as the TFTprocess (so-called aSi-liquid crystal panel).

The technology of the present disclosure described below can be appliedto any display system of the transmissive type, the reflective type, andthe semi-transmissive type, and can be applied to a case where theliquid crystal mode is any of the VA mode and the TN mode. Moreover, thetechnology of the present disclosure can also be applied to a case wherethe material of the thin film transistor is any of silicon, transparentoxide semiconductor, and organic semiconductor.

<Basic Configuration of Liquid Crystal Display Device>

The basic configuration of the liquid crystal display device of thepresent disclosure will be described by taking an active matrix liquidcrystal display device as an example. The active matrix liquid crystaldisplay device is a display device of a so-called active matrix drivesystem in which an independent pixel electrode is disposed in each pixeland a switching element is connected to each pixel electrode toselectively drive the pixels.

In the active matrix liquid crystal display device, a liquid crystalpanel is configured by enclosing liquid crystal between two substrates,that is, a first substrate and a second substrate. The first substrateis, for example, a thin film transistor (TFT) substrate on which a TFTis formed as a switching element. The second substrate is a countersubstrate on which a color filter, a counter electrode, and the like areformed and which faces the TFT substrate. Then, in the liquid crystalpanel, liquid crystal alignment is controlled by switching controlperformed by the switching element and voltage application based on avideo signal, and video display is performed by changing lighttransmittance/reflectance.

[System Configuration]

FIG. 1 illustrates an example of the system configuration of the activematrix liquid crystal display device. As illustrated in FIG. 1, theactive matrix liquid crystal display device according to the presentexample includes a pixel array section 20 in which pixels 10 aretwo-dimensionally arranged in a row direction and a column direction,and a pixel drive unit that drives each pixel 10 of the pixel arraysection 20. The pixel drive unit includes a scan line drive unit 30, asignal line drive unit 40, and the like.

The pixel array section 20 has a pixel array of m rows and n columns.For this pixel arrangement of m rows and n columns, scan lines 51 ₁ to51 _(m) (hereinafter sometimes collectively referred to as a “scan line51”) are wired for each pixel row, and signal lines 52 ₁ to 52 _(n)(hereinafter, sometimes collectively referred to as a “signal line 52”)are wired for each pixel column. One end of the scan line 51 isconnected to an output end in the corresponding row of the scan linedrive unit 30. One end of the signal line 52 is connected to an outputend in the corresponding column of the signal line drive unit 40.

(V_(com) Inversion Driving)

In the active matrix liquid crystal display device having theconfiguration described above, so-called AC driving is performed inwhich the voltage applied to the liquid crystal is inverted with thereference voltage as a center at a constant cycle by using an AC drivenanalog video signal. Here, the “AC driven analog video signal” refers toan analog video signal whose polarity is inverted at a predeterminedcycle centered on a reference voltage V_(com) (hereinafter, referred toas a “common voltage V_(com)”). The common voltage V_(com) is applied tothe counter electrode (common electrode) of the liquid crystal unit.

In the case of AC driving, an AC driven analog video signal, that is, apositive polarity video signal and a negative polarity video signal arealternately supplied from the signal line drive unit 40 to the signallines 52 ₁ to 52 _(n). Furthermore, in the active matrix liquid crystaldisplay device according to this example, so-called V_(com) inversiondriving is adopted in which the polarity of the common voltage V_(com)applied to the counter electrode of the liquid crystal unit isperiodically inverted in synchronization with the positive polarityvideo signal and the negative polarity video signal.

(Surface Collective Driving)

In the V_(com) inversion driving liquid crystal display device, as adrive system of each pixel 10 of the pixel array section 20, surfacecollective driving is known in which all the pixels 10 of the pixelarray section 20 are driven simultaneously (collectively) with respectto the entire screen. According to this surface collective driving, itis possible to suppress image interference due to line-sequentialdriving in which driving is performed sequentially in units of rows fromthe upper part to the lower part of the screen.

In order to realize surface collective driving, a configuration isadopted in which two storage capacitors are provided in the pixelcircuit, and a positive polarity video signal and a negative polarityvideo signals are separately held in the storage capacitors of the twosystems, and held voltages of the storage capacitors are alternatelyapplied to the pixel electrodes of the liquid crystal unit. Therefore,since the voltages applied to the pixel electrode can be held in thestorage capacitors of the respective two systems for one display frameperiod, the AC drive frequency in the V_(com) inversion driving can beset to any value independently of the vertical scanning frequency.

As an example, considering a liquid crystal display device driven at 60Hz, the driving speed is 120 Hz in the case of double speed driving.However, in the case of 60 Hz driving, if surface collective driving isperformed for each color of red R, green G, and blue B, it is necessaryto output video signals of respective RGB colors in the period of onecycle of 60 Hz. Therefore, for example, driving at 180 Hz (=60 Hz×3 (for3 RGB colors)) is performed. As described above, by adopting the surfacecollective driving using the two-system storage capacitors, the AC drivefrequency in V_(com) inversion driving can be set to any frequencyregardless of the vertical scanning frequency.

Pixel Circuit According to Reference Example

In the following, a pixel circuit for realizing surface collectivedriving in a V_(com) inversion driving liquid crystal display devicewill be described. FIG. 2 illustrates a circuit example of a pixelcircuit according to a reference example, which is a premise of thetechnology of the present disclosure. FIG. 2 illustrates a pixel circuitfor one pixel. Here, a case where the liquid crystal mode (liquidcrystal molecule arrangement) is a normally black VA mode will bedescribed as an example.

A liquid crystal unit (liquid crystal element) 60 includes a pixelelectrode 61, a counter electrode (common electrode) 62 facing the pixelelectrode 61, and a liquid crystal layer 63 sealed between the pixelelectrode 61 and the counter electrode 62. A common voltage V_(com)whose polarity is periodically inverted in synchronization with polarityinversion of a video signal V_(sig) is applied to the counter electrode62 in common for all the pixels.

The video signal V_(sig) whose polarity is periodically inverted issupplied to the pixel (pixel circuit) through a signal line 52. A drivecircuit unit that drives the liquid crystal unit 60 includes a firstwriting circuit 70 ₁ that writes a positive (so-called a positive (P)phase) video signal and a second writing circuit 70 ₂ that writes anegative (so-called a negative (N) phase) video signal.

The first writing circuit 70 ₁ includes a first transfer transistor 71_(1_n), a storage capacitor 72 ₁, and a second transfer transistor 73_(1_n). Each of the first transfer transistor 71 _(1_n) and the secondtransfer transistor 73 _(1_n) is an N-channel MOS transistor. One of thesource and drain electrodes of the first transfer transistor 71 _(1_n)is connected to the signal line 52. One end of the storage capacitor 72₁ and one of the source and drain electrodes of the second transfertransistor 73 _(1_n) are connected to the other of the source and drainelectrodes of the first transfer transistor 71 _(1_n). The other end ofthe storage capacitor 72 ₁ is connected to a ground GND which is a nodeof a reference potential. The other of the source and drain electrodesof the second transfer transistor 73 _(1_n) is connected to the pixelelectrode 61 of the liquid crystal unit 60.

Basically, the second writing circuit 70 ₂ also has a similar circuitconfiguration as that of the first writing circuit 70 ₁. That is, thesecond writing circuit 70 ₂ includes a first transfer transistor 71_(2_n), a storage capacitor 72 ₂, and a second transfer transistor 73_(2_n). Each of the first transfer transistor 71 _(2_n) and the secondtransfer transistor 73 _(2_n) is an N-channel MOS transistor. One of thesource and drain electrodes of the first transfer transistor 71 _(2_n)is connected to the signal line 52. One end of the storage capacitor 72₂ and one of source and drain electrodes of the second transfertransistor 73 _(2_n) are connected to the other of the source and drainelectrodes of the first transfer transistor 71 _(2_n). The other end ofthe storage capacitor 72 ₂ is connected to a ground GND. The other ofthe source and drain electrodes of the second transfer transistor 73_(2_n) is connected to the pixel electrode 61 of the liquid crystal unit60.

As described above, the pixel circuit according to the reference examplehas a configuration in which all the first writing circuit 70 ₁ thatwrites a positive (P phase) video signal and the second writing circuit70 ₂ that writes a negative (N phase) video signal are N-channel MOStransistors. In the case of considering a pixel circuit of surfacecollective driving, it is fundamental to configure the circuit only withN-channel MOS transistors having high driving ability and high areaefficiency.

However, in the case of configuring the circuit only with N channel typeMOS transistors, since not only coupling with the storage capacitors 72₁, 72 ₂ but also voltage drop due to the threshold voltage V_(th) of theN-channel MOS transistors have an influence, the writing voltage to thepixel is lowered. This lowering of the write voltage leads to loweringof a liquid crystal drive voltage on the negative polarity side (Nphase). As a result, the reflectance is lowered and the voltagewaveforms of the N-phase and P-phase liquid crystal drive voltages areunbalanced.

FIG. 3A illustrates voltage waveforms of a video signal V_(sig) and acommon voltage V_(com) during white display and FIG. 3B illustratesvoltage waveforms of a video signal V_(sig) and a common voltage V_(com)during black display, in a pixel circuit according to the referenceexample.

Note that here, the case where the liquid crystal mode is the normallyblack VA mode has been described as an example; however, in a case wherethe liquid crystal mode is the normally white TN mode, the transmittanceis lowered due to lowering of the liquid crystal drive voltage.

Liquid Crystal Display Device According to Embodiment

In the liquid crystal display device according to the embodiment of thepresent disclosure, in order to eliminate the above-described adverseeffect caused by using only N-channel MOS transistors as the transistorsforming the first writing circuit 70 ₁ and the second writing circuit 70₂, the following configuration is adopted. That is, since a firstwriting circuit 70 ₁ and a second writing circuit 70 ₂ are configured byusing transistors having conductivity types different from each other,the writing voltage to a pixel is prevented from lowering due to athreshold voltage V_(th) of the transistors included in the firstwriting circuit 70 ₁ and the second writing circuit 70 ₂.

Hereinafter, a specific example of the present embodiment for preventingthe writing voltage to the pixel from lowering due to the thresholdvoltage V_(th) of the transistors included in the first writing circuit70 ₁ and the second writing circuit 70 ₂ will be described.

Example 1

Example 1 is an example in which the liquid crystal mode is the VA mode.A circuit example of the pixel circuit according to Example 1 isillustrated in FIG. 4. FIG. 4 illustrates a pixel circuit for one pixel.

A liquid crystal unit (liquid crystal element) 60 includes a pixelelectrode 61, a counter electrode (common electrode) 62 facing the pixelelectrode 61, and a liquid crystal layer 63 sealed between the pixelelectrode 61 and the counter electrode 62. A common voltage V_(com)whose polarity is periodically inverted in synchronization with polarityinversion of a video signal V_(sig) is applied to the counter electrode62 in common for all the pixels.

The first writing circuit 70 ₁ includes a first transfer transistor 71_(1_n), a storage capacitor 72 ₁, and a second transfer transistor 73_(1_n). Each of the first transfer transistor 71 _(1_n) and the secondtransfer transistor 73 _(1_n) is an N-channel MOS transistor. One of thesource and drain electrodes of the first transfer transistor 71 _(1_n)is connected to the signal line 52. One end of the storage capacitor 72₁ and one of the source and drain electrodes of the second transfertransistor 73 _(1_n) are connected to the other of the source and drainelectrodes of the first transfer transistor 71 _(1_n). The other end ofthe storage capacitor 72 ₁ is connected to a ground GND which is areference potential. The other of the source and drain electrodes of thesecond transfer transistor 73 _(1_n) is connected to the pixel electrode61 of the liquid crystal unit 60.

The second writing circuit 70 ₂ includes a first transfer transistor 71_(2_p), a storage capacitor 72 ₂, and a second transfer transistor 73_(2_p). The first transfer transistor 71 _(2_p), and the second transfertransistor 73 _(2_p) are P-channel MOS transistors. One of the sourceand drain electrodes of the first transfer transistor 71 _(2_p), isconnected to the signal line 52. One end of the storage capacitor 72 ₂and one of source and drain electrodes of the second transfer transistor73 _(2_p) are connected to the other of the source and drain electrodesof the first transfer transistor 71 _(2_p). The other end of the storagecapacitor 72 ₂ is connected to a ground GND. The other of the source anddrain electrodes of the second transfer transistor 73 _(2_p) isconnected to the pixel electrode 61 of the liquid crystal unit 60.

As described above, the pixel circuit according to Example 1 has aconfiguration in which in the case of the VA mode, N-channel MOStransistors are used as the transistors configuring the first writingcircuit 70 ₁ that writes a P-phase video signal, and P-channel MOStransistors are used as the transistors configuring the second writingcircuit 70 ₂ that writes an N-phase video signal.

FIG. 5A illustrates voltage waveforms of a video signal V_(sig) and acommon voltage V_(com) during white display and FIG. 5B illustratesvoltage waveforms of a video signal V_(sig) and a common voltage V_(com)during black display, in the pixel circuit according to Example 1.

In the case of the VA mode, since P-channel MOS transistors are used toconfigure the second writing circuit 70 ₂ that writes an N-phase videosignal, it is possible to prevent a writing voltage to the pixel in theN-phase from lowering at the time of writing the video signal.Therefore, a liquid crystal drive voltage is prevented from lowering.Therefore, in the pixel circuit of surface collective driving, it ispossible to apply the maximum voltage as the liquid crystal drivevoltage with a small number of transistors, that is, two first writingcircuit 70 ₁ and two second writing circuits 70 ₂, in a total of fourtransistors, without being affected by the threshold voltage V_(th) ofthe transistor. Moreover, since it is possible to prevent the liquidcrystal drive voltage from decreasing in the N phase, it is possible tomaintain the balance of the voltage waveforms of the N-phase and P-phaseliquid crystal drive voltages, and thus it is possible to obtain a gooddisplay image.

FIG. 6 illustrates a voltage-reflectance/transmittance characteristic ofliquid crystal. As is clear from FIG. 6, thevoltage-reflectance/transmittance characteristic of liquid crystal alsohas a threshold voltage. Therefore, in the pixel circuit according toExample 1, it is preferable to set the threshold voltage V_(th) of thefirst transfer transistors 71 _(1_n), 71 _(2_p) of the first writingcircuit 70 ₁ and the second writing circuit 70 ₂ to be equal to or lessthan the threshold voltage of the voltage-reflectance/transmittancecharacteristic of liquid crystal.

Incidentally, on the side where the reflectance is low, both the N phaseand the P phase are affected by the threshold voltage V_(th) of thefirst transfer transistors 71 _(1_n), 71 _(2_p), and the video signalV_(sig) rises by the threshold voltage V_(th). In contrast, in the pixelcircuit according to the first embodiment, as described above, thethreshold voltage V_(th) of the first transfer transistors 71 _(1_n), 71_(2_p) is set to be equal to or lower than the threshold voltage of thevoltage-reflectance/transmittance characteristic of the liquid crystal.As a result, even if the video signal V_(sig) rises by the thresholdvoltage V_(th), the liquid crystal does not move. Therefore, display isdarkened on the side where the reflectance is low, that is, the blackdisplay becomes a darker black display.

Example 2

Example 2 is an example in which the liquid crystal mode is the TN mode.A circuit example of the pixel circuit according to Example 2 isillustrated in FIG. 7. FIG. 7 illustrates a pixel circuit for one pixel.

In the first writing circuit 70 ₁, the first transfer transistor 71_(1_n) and the second transfer transistor 73 _(1_n) are P-channel MOStransistors. One of the source and drain electrodes of the firsttransfer transistor 71 _(1_n) is connected to the signal line 52. Oneend of the storage capacitor 72 ₁ and one of the source and drainelectrodes of the second transfer transistor 73 _(1_n) are connected tothe other of the source and drain electrodes of the first transfertransistor 71 _(1_n). The other end of the storage capacitor 72 ₁ isconnected to a ground GND which is a reference potential. The other ofthe source and drain electrodes of the second transfer transistor 73_(1_n) is connected to the pixel electrode 61 of the liquid crystal unit60.

In the second writing circuit 70 ₂, the first transfer transistor 71_(2_n) and the second transfer transistor 73 _(2_n) are N-channel MOStransistors. One of the source and drain electrodes of the firsttransfer transistor 71 _(2_n) is connected to the signal line 52. Oneend of the storage capacitor 72 ₂ and one of source and drain electrodesof the second transfer transistor 73 _(2_n) are connected to the otherof the source and drain electrodes of the first transfer transistor 71_(2_n). The other end of the storage capacitor 72 ₂ is connected to aground GND. The other of the source and drain electrodes of the secondtransfer transistor 73 _(2_n) is connected to the pixel electrode 61 ofthe liquid crystal unit 60.

Also in the pixel circuit according to Example 2 having theconfiguration described above, the operation and effect similar to thosein the pixel circuit according to Example 1 can be obtained. That is, inthe case of the TN mode, since the P-channel MOS transistor is used toconfigure the first writing circuit 70 ₁ that writes a P-phase videosignal, it is possible to prevent the liquid crystal drive voltage fromlowering. Therefore, since the maximum voltage can be applied as theliquid crystal drive voltage without being affected by the thresholdvoltage V_(th) of the transistors, and the balance of the voltagewaveforms of the N-phase and P-phase liquid crystal drive voltages canbe maintained, a good display image can be obtained.

Example 3

Example 3 is a modification of Example 1 and is an example in which atransfer gate is used as the first transfer transistor. A circuitexample of the pixel circuit according to Example 3 is illustrated inFIG. 8. FIG. 8 illustrates a pixel circuit for one pixel.

In the pixel circuit according to Example 3, the first writing circuit70 ₁ and the second writing circuit 70 ₂ are configured such that eachof the first transfer transistors 71 _(1_n), 71 _(2_n) is a transfergate in which an N-channel transistor and a P-channel transistor areconnected in parallel. According to the pixel circuit of Example 3,although the number of transistors is increased as compared with that inthe Example 1 in which each of the first transfer transistors 71 _(1_n),71 _(2_n) includes a single transistor, there is an advantage that thedriving capability can be increased.

Here, Example 3 has been described as a modification of Example 1 in theVA mode. Similarly, as a modification of Example 2 of the TN mode, aconfiguration may be adopted where the first transfer transistors 71_(1_n), 71 _(2_n) of the first writing circuit 70 ₁ and the secondwriting circuit 70 ₂ are transfer gates. Furthermore, the first transfertransistor 71 _(2_n) and the second transfer transistor 73 _(2_n) in theP-phase second writing circuit 70 ₂ can also include transfer gates.

Example 4

Example 4 is an example of an LCOS device in which liquid crystal isdisposed on a semiconductor substrate. The LCOS device is a device inwhich a liquid crystal layer is sandwiched between a silicon substrateand a transparent substrate.

FIG. 9 illustrates an example of a sectional structure of the LCOSdevice according to Example 4. The LCOS device has a structure in whicha liquid crystal drive circuit unit 70 and a pixel electrode 61 areformed on a silicon substrate 81, and a liquid crystal layer 63 issandwiched by a transparent substrate 82 such as a glass substratehaving a counter electrode 62 on an inner surface thereof. The pixelelectrode 61 is a reflective electrode including aluminum or the like.The counter electrode 62 is a transparent electrode including indium tinoxide (IOT) or the like. An alignment layer 64 is interposed between thepixel electrode 61 and the liquid crystal layer 63, and an alignmentlayer 65 is interposed between the liquid crystal layer 63 and thecounter electrode 62. Then, light having passed through the counterelectrode 62 which is a transparent substrate and the liquid crystallayer 63 is reflected by the pixel electrode 61, which is a reflectiveelectrode.

In the LCOS device, the storage capacitors 72 ₁, 72 ₂ can have a gatecapacitance structure formed between the gate electrodes of the firsttransfer transistors 71 _(1_n), 71 _(1_p) or the second transfertransistors 73 _(1_n), 73 _(1_p) and the silicon substrate, or ametal-insulator-metal (MIM) structure formed on the wiring. Inparticular, in order to reduce the pixel pitch, it is preferable thateach of the storage capacitors 72 ₁, 72 ₂ has the MIM structure.

<Electronic Apparatus of Present Disclosure>

The liquid crystal display device of the present disclosure describedabove can be used as a display unit (display device) of an electronicapparatus in any field that displays a video signal input to theelectronic apparatus, or a video signal generated in the electronicapparatus, as an image or video. For example, the liquid crystal displaydevice can be used as a display unit of a projection-type display device(projector), a head mounted display, a digital still camera, a videocamera, a mobile terminal device such as a mobile phone, a laptoppersonal computer, a television set, or the like.

The liquid crystal display device of the present disclosure alsoincludes a module-shaped device having a sealed configuration. Anexample of the module-shaped device is a display module formed byattaching a facing portion such as transparent glass to a pixel arraysection. Note that the display module may have a configuration in whicha circuit unit for inputting and outputting a signal or the like fromthe outside to the pixel array section, a flexible printed circuit(FPC), or the like is provided.

The liquid crystal display device of the present disclosure, that is, aV_(com) inversion drive liquid crystal display device that realizessurface collective driving by using the storage capacitors of twosystems can apply a maximum voltage as a liquid crystal drive voltageand at the same time the balance between voltage waveforms of N-phaseand P-phase liquid crystal drive voltages can be maintained. Therefore,a good display image can be obtained by using the liquid crystal displaydevice of the present disclosure as a display unit (liquid crystalpanel) of the electronic apparatus.

Hereinafter, a projection-type display device (projector) and a headmounted display will be illustrated as specific examples of theelectronic apparatus using the liquid crystal display device of thepresent disclosure. However, the specific examples illustrated here areexamples only, and it is not limited to them.

Specific Example 1

FIG. 10 is a schematic configuration diagram illustrating a basicconfiguration of a projection-type display device (projector) accordingto Specific example 1 of the electronic apparatus of the presentdisclosure. Here, as the projection-type display device, a single-plateprojection-type display device is described as an example.

A single-plate projection-type display device (projector) 100 accordingto the present Specific example 1 includes a light source 101, a liquidcrystal panel (display unit) 102, a beam splitter 103, and a projectionlens 104. The light source 101 repeatedly emits light in each color of,for example, R (red), G (green), and B (blue), which is necessary fordisplaying a color image, in a predetermined cycle. Light in each coloremitted from the light source 101 is applied to the liquid crystal panel102 through the beam splitter 103.

The liquid crystal panel 102 includes, for example, an LCOS device. Asthe liquid crystal panel 102, it is possible to use the liquid crystaldisplay device according to the present disclosure, that is, a V_(com)inversion drive liquid crystal display device that realizes surfacecollective driving by using the storage capacitors of two systems. Rimage light, G image light, and B image light are sequentially emittedfrom the liquid crystal panel 102 with a time difference, and are guidedto the projection lens 104 through the beam splitter 103. The projectionlens 104 projects the R image light, the G image light, and the B imagelight, which are sequentially emitted from the liquid crystal panel 102,toward a screen 110.

As described above, in the single-plate projection-type display device100 that uses as the liquid crystal panel 102, the V_(com) inversionliquid crystal display device that realizes surface collective drivingusing the storage capacitors of two systems, the R image light, the Gimage light, and the B image light emitted sequentially from the liquidcrystal panel 102 are projected on the screen 110 with a timedifference. Then, the R image, the G image, and the B image projected onthe screen 110 with a time difference are synthesized in human eyes andare recognized as a color image.

Note that here, a case where the liquid crystal display device accordingto the present disclosure is used as the liquid crystal panel in thesingle-plate projection-type display device has been described as anexample. However, the liquid crystal display device according to thepresent disclosure is applied not only to the single-plateprojection-type display device, and the liquid crystal display deviceaccording to the present disclosure can be used as a liquid crystalpanel in a three-plates projection display device. In a case of beingapplied to the three-plates projection-type display device, liquidcrystal display devices corresponding to R, G, and B colors are used asthree liquid crystal panels, and color display is realized bysynthesizing images on the three plates. Furthermore, although areflection type device is used as the liquid crystal panel 102 here, atransmissive-type device can also be used.

Specific Example 2

FIG. 11 is an external view illustrating an example of a head mounteddisplay according to Specific example 2 of the electronic apparatus ofthe present disclosure.

A head mounted display 200 according to the present Specific example 2has a transmissive head mounted display configuration including a mainbody section 201, an arm section 202, and a lens barrel 203. The mainbody section 201 is connected to the arm section 202 and eyeglasses 210.Specifically, an end portion in the long side direction of the main bodysection 201 is attached to the arm section 202. Furthermore, one sidesurface of the main body section 201 is connected to the eyeglasses 210through a connecting member (not illustrated). Note that the main bodysection 201 may be directly mounted to the head of a human body.

The main body section 201 includes a control board for controllingoperation of the head mounted display 200 and a display unit. The armsection 202 supports the lens barrel 203 with respect to the main bodysection 201 by connecting the main body section 201 and the lens barrel203. Specifically, the arm section 202 fixes the lens barrel 203 to themain body section 201 by being coupled to the end portion of the mainbody section 201 and an end portion of the lens barrel 203. Furthermore,the arm section 202 incorporates a signal line for communicating dataregarding an image provided from the main body section 201 to the lensbarrel 203.

The lens barrel 203 projects image light provided from the main bodysection 201 via the arm section 202 through a lens 211 of the eyeglasses210 toward an eye of the user wearing the head mounted display 200. Inthis head mounted display 200, as the liquid crystal display deviceaccording to the present disclosure, that is, the V_(com) inversiondrive liquid crystal display device that realizes surface collectivedriving by using the storage capacitors of two systems can be used asthe display unit incorporated in the main body section 201.

<Configurations that Present Disclosure can Take>

Note that the present disclosure can also be configured as follows.

<<A. Display Device>>

[A-1] A liquid crystal display device including:

a liquid crystal unit including a pixel electrode, a counter electrodefacing the pixel electrode, and a liquid crystal layer sealed betweenthe pixel electrode and the counter electrode;

a first writing circuit configured to write a positive polarity videosignal among video signals whose polarity changes periodically; and

a second writing circuit configured to write a negative polarity videosignal among the video signals whose polarity changes periodically,

the liquid crystal unit, the first writing circuit, and the secondwriting circuit provided for each pixel, and

the first writing circuit and the second writing circuit includingtransistors having conductivity types different from each other.

[A-2] The liquid crystal display device according to the [A-1], in which

a common voltage whose polarity is periodically inverted insynchronization with a positive polarity video signal and a negativepolarity video signal is applied to the counter electrode of the liquidcrystal unit in common for all the pixels.

[A-3] The liquid crystal display device according to the [A-2], in which

the first writing circuit and the second writing circuit include storagecapacitors that hold a positive polarity video signal and a negativepolarity video signal, respectively.

[A-4] The liquid crystal display device according to the [A-3], in which

the first writing circuit and the second writing circuit include

first transfer transistors that alternately write a positive polarityvideo signal and a negative polarity video signal to the storagecapacitors, and

second transfer transistors that alternately apply held voltages of thestorage capacitors to the pixel electrode of the liquid crystal unit,collectively for all the pixels, respectively.

[A-5] The liquid crystal display device according to the [A-4], in which

in a case where a liquid crystal mode is a VA mode,

each of the first transfer transistor and the second transfer transistorof the first writing circuit includes an N-channel transistor, and

each of the first transfer transistor and the second transfer transistorof the second writing circuit includes a P-channel transistor.

[A-6] The liquid crystal display device according to the [A-4], in which

in a case where the liquid crystal mode is a TN mode,

each of the first transfer transistor and the second transfer transistorof the first writing circuit includes a P-channel transistor, and

each of the first transfer transistor and the second transfer transistorof the second writing circuit includes an N-channel transistor.

[A-7] The liquid crystal display device according to the [A-5] or the[A-6], in which

a threshold voltage of the first transfer transistor of each of thefirst writing circuit and the second writing circuit is set to be equalto or lower than a threshold voltage of avoltage-reflectance/transmittance characteristic of liquid crystal.

[A-8] The liquid crystal display device according to the [A-7], in which

the first transfer transistor of each of the first writing circuit andthe second writing circuit includes a transfer gate in which anN-channel transistor and a P-channel transistor are connected inparallel.

[A-9] The liquid crystal display device according to any one of the[A-1] to the [A-8], in which

the liquid crystal unit, the first writing circuit, and the secondwriting circuit are formed on a semiconductor substrate.

<<B. Electronic Apparatus>>

[B-1] An electronic apparatus including a liquid crystal display deviceincluding

a liquid crystal unit including a pixel electrode, a counter electrodefacing the pixel electrode, and a liquid crystal layer sealed betweenthe pixel electrode and the counter electrode,

a first writing circuit configured to write a positive polarity videosignal among video signals whose polarity changes periodically, and

a second writing circuit configured to write a negative polarity videosignal among the video signals whose polarity changes periodically,

the liquid crystal unit, the first writing circuit, and the secondwriting circuit provided for each pixel, and

the first writing circuit and the second writing circuit includingtransistors having conductivity types different from each other.

[B-2] The electronic apparatus according to the [B-1], in which

a common voltage whose polarity is periodically inverted insynchronization with a positive polarity video signal and a negativepolarity video signal, is applied to the counter electrode of the liquidcrystal unit in common for all the pixels.

[B-3] The electronic apparatus according to the [B-2], in which

the first writing circuit and the second writing circuit include storagecapacitors that hold a positive polarity video signal and a negativepolarity video signal, respectively.

[B-4] The electronic apparatus according to the [B-3], in which

the first writing circuit and the second writing circuit include

first transfer transistors that alternately write a positive polarityvideo signal and a negative polarity video signal to the storagecapacitors, and

second transfer transistors that alternately apply the held voltages ofthe storage capacitors to the pixel electrode of the liquid crystalunit, collectively for all pixels.

[B-5] The electronic apparatus according to the [B-4], in which

in a case where a liquid crystal mode is a VA mode,

each of the first transfer transistor and the second transfer transistorof the first writing circuit includes an N-channel transistor, and

each of the first transfer transistor and the second transfer transistorof the second writing circuit includes a P-channel transistor.

[B-6] The liquid crystal display device according to the [B-4], in which

in a case where a liquid crystal mode is a TN mode,

each of the first transfer transistor and the second transfer transistorof the first writing circuit includes a P-channel transistor, and

each of the first transfer transistor and the second transfer transistorof the second writing circuit includes an N-channel transistor.

[B-7] The electronic apparatus according to the [B-5] or the [B-6], inwhich

a threshold voltage of the first transfer transistor of each of thefirst writing circuit and the second writing circuit is set to be equalto or lower than a threshold voltage of avoltage-reflectance/transmittance characteristic of liquid crystal.

[B-8] The electronic apparatus according to the [B-7], in which

the first transfer transistor of each of the first writing circuit andthe second writing circuit includes a transfer gate in which anN-channel transistor and a P-channel transistor are connected inparallel.

[B-9] The electronic apparatus according to any one of the [B-1] to the[B-8], in which

the liquid crystal unit, the first writing circuit, and the secondwriting circuit are formed on a semiconductor substrate.

REFERENCE SIGNS LIST

-   10 Pixel-   20 Pixel array section-   30 Scan line drive unit-   40 Signal line drive unit-   51(51 ₁ to 51 _(m)) Scan line-   52(52 ₁ to 52 _(m)) Signal line-   60 Liquid crystal unit (liquid crystal element)-   61 Pixel electrode-   62 Counter electrode (Common electrode)-   63 Liquid crystal layer-   70 ₁ First writing circuit-   70 ₂ Second writing circuit-   71 _(1_n), 71 _(2_p) First transfer transistor-   72 ₁, 72 ₂ Storage capacitor-   73 _(1_n), 73 _(2_p) Second transfer transistor

1. A liquid crystal display device comprising: a liquid crystal unitincluding a pixel electrode, a counter electrode facing the pixelelectrode, and a liquid crystal layer sealed between the pixel electrodeand the counter electrode; a first writing circuit configured to write apositive polarity video signal among video signals whose polaritychanges periodically; and a second writing circuit configured to write anegative polarity video signal among the video signals whose polaritychanges periodically, the liquid crystal unit, the first writingcircuit, and the second writing circuit provided for each pixel, and thefirst writing circuit and the second writing circuit includingtransistors having conductivity types different from each other.
 2. Theliquid crystal display device according to claim 1, wherein a commonvoltage whose polarity is periodically inverted in synchronization witha positive polarity video signal and a negative polarity video signal isapplied to the counter electrode of the liquid crystal unit in commonfor all the pixels.
 3. The liquid crystal display device according toclaim 2, wherein the first writing circuit and the second writingcircuit include storage capacitors that hold a positive polarity videosignal and a negative polarity video signal, respectively.
 4. The liquidcrystal display device according to claim 3, wherein the first writingcircuit and the second writing circuit include first transfertransistors that alternately write a positive polarity video signal anda negative polarity video signal to the storage capacitors, and secondtransfer transistors that alternately apply held voltages of the storagecapacitors to the pixel electrode of the liquid crystal unit,collectively for all the pixels, respectively.
 5. The liquid crystaldisplay device according to claim 4, wherein in a case where a liquidcrystal mode is a VA mode, each of the first transfer transistor and thesecond transfer transistor of the first writing circuit includes anN-channel transistor, and each of the first transfer transistor and thesecond transfer transistor of the second writing circuit includes aP-channel transistor.
 6. The liquid crystal display device according toclaim 4, wherein in a case where a liquid crystal mode is a TN mode,each of the first transfer transistor and the second transfer transistorof the first writing circuit includes a P-channel transistor, and eachof the first transfer transistor and the second transfer transistor ofthe second writing circuit includes an N-channel transistor.
 7. Theliquid crystal display device according to claim 5, wherein a thresholdvoltage of the first transfer transistor of each of the first writingcircuit and the second writing circuit is set to be equal to or lowerthan a threshold voltage of a voltage-reflectance/transmittancecharacteristic of liquid crystal.
 8. The liquid crystal display deviceaccording to claim 7, wherein the first transfer transistor of each ofthe first writing circuit and the second writing circuit includes atransfer gate in which an N-channel transistor and a P-channeltransistor are connected in parallel.
 9. The liquid crystal displaydevice according to claim 1, wherein the liquid crystal unit, the firstwriting circuit, and the second writing circuit are formed on asemiconductor substrate.
 10. An electronic apparatus comprising a liquidcrystal display device including a liquid crystal unit including a pixelelectrode, a counter electrode facing the pixel electrode, and a liquidcrystal layer sealed between the pixel electrode and the counterelectrode, a first writing circuit configured to write a positivepolarity video signal among video signals whose polarity changesperiodically, and a second writing circuit configured to write anegative polarity video signal among the video signals whose polaritychanges periodically, the liquid crystal unit, the first writingcircuit, and the second writing circuit provided for each pixel, and thefirst writing circuit and the second writing circuit includingtransistors having conductivity types different from each other.